I have included links to 2 RAW images ( I've also put the JPEG images up) that I took in Iceland last month where I was very fortunate to see the northern lights on two different nights. The photographs are far from perfect as I’m new to photography but there are two my main issues. On the first night there was a very bright full moon which has left the sky too light (photograph called Lights). I would like to darken the sky and give it more a night time look without losing the colour of the northern lights or the detail of the mountain.

On the second night the lights came out unexpectedly while I was driving and in my haste to set up I forgot that I still had a polarising filter on the lens so everything in the photograph is a bit dark and dull (photograph called Polarised).

You have enough reputation for images now. Inlining 'em would help, especially for people without NEF viewers on their system. (And, particularly, to point out any differences in the situation from the earlier question.)
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mattdmApr 16 '13 at 15:46

It does help partially but there is a difference, especially in the photograph with the bright moonlight.
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TimApr 16 '13 at 19:10

I find this question and answers more helpful than the older one mentioned by mattdm. Is it possible to merge an older question with a newer one, rather than vice-versa?
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Michael ClarkApr 16 '13 at 19:31

1

@MichaelClark A mod can do that, although if the questions aren't literally identical it gets messy and it's probably best to just leave them separate with links. (And the shared aurora-borealis tag.)
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mattdmApr 16 '13 at 20:04

1 Answer
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There is a little bit different here than in the linked potential duplicate. The Polarized image is roughly the same situation, but the other shot with the moon is a bit different.

I applied similar edits to the Aurora from the linked question to get this result with the polarized version:

There is actually quite a bit of detail in the shadows. Even at ISO 800, you still have about 10 stops of dynamic range, which is still quite a bit. The image above uses the following LR4 adjustments:

Exposure: +1.5

Highlights: -75

Shadows: +100

Whites: 0

Blacks: +100

Clarity: +80

Tone Curve:

Highlights: +10

Lights: +25

Darks: -30

Shadows: -10

Luminance NR:

Luminance: 70

Detail: 65

Your image was rather out of focus. This is evidenced by the stars, which all have a coma-like stretch to them. It is quite visible in the landscape as well. Focus at night is best done on stars with Live View, and all you need is one bright star to do it. Once you focus on a star, you will have what is roughly infinity focus, and stopping down will help clear up the whole field. Just to demonstrate how far you can push this image:

The changes from above are as follows:

Exposure: +3.0

Contrast: +55

Highlights: -100

Shadows: +100

Whites: -60

Blacks: +90

Clarity: +80

Tone Curve:

Highlights: 0

You can see that even when a photo looks severely underexposed, modern cameras have quite a lot of editing latitude. You can extract a lot of detail from those shadows. There IS a fair bit of noise, but since the image was defocused anyway, it was easy to clean up.

The moonlit aurora image is a bit more difficult. The trick is to make the sky look darker, while concurrently lifting the shadows in the foreground. Two tools can be of help here: Clarity and the Tone Curve. Clarity is a microcontrast tool. Unlike the Contrast slider, which affects global contrast, clarity works around objects and areas to increase their contrast relative to each other. A strong Clarity push will help darken the sky, but you can't push it too much, otherwise the foreground will start to look funky. Additionally, the Tone Curve can be used to control how the tones of the image are redistributed, to ensure that highlights and whites affect the right parts of the image, allowing the shadows to be usefully recovered:

The edits for the above image are as follows:

Exposure: +1

Highlights: -100

Shadows: +100

Whites: +50

Blacks: -15

Clarity: +60

Tone Curve:

Split:

Highlight: 55

Midtone: 35

Shadow: 18

Curve:

Highlight: +40

Lights: -40

Darks: -55

Shadows: +60

The key thing to notice here are the tone curve edits. In addition to adjusting the curve itself, I also adjusted the splits in the curve. I moved the range for highlights from the default 75 down to 55. That makes the highlight end of the curve affect a much greater range of brighter tones in the image than it does by default. I also moved midtones and shadows down a little as well. Additionally, I did an inverse change, by LIFTING the shadow part of the curve. These edits allow you to more finely control what adjustments affect what tonal ranges of your image, giving you more control over highlights, whites, midtones, darks, and shadows. The extremely dull and flat original NEF turned out to be fairly nice and contrasty in the end.

That's a huge improvement. Thanks for the help. They are out of focus, it was my first attempt at photographing the northern lights and I was having trouble finding focus at night. I'll try your tip next time.
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TimApr 16 '13 at 19:15

A quick note about photographing Aurora. Similar to photographing Meteor Showers, the trick is to normalize "time on pixels" for the aurora and the stars. An aurora is very dim, and it moves across the frame faster than the stars do. The best way to maximize the potential of a shot is to use a higher ISO. Don't be afraid to push as high as ISO 3200 on most cameras. If you have one of Canon's newer cameras like the 1D X, 5D III, or 6D...you could even use ISO 12800! That would get you a much richer exposure, and possibly even allow you to stop down a third of a stop or two for sharper results.
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jrista♦Apr 18 '13 at 16:44